using System;
//using Org.BouncyCastle.Math;
//using Org.BouncyCastle.Security;
using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Crypto.Parameters;

namespace Org.BouncyCastle.Crypto.Generators
{
    /**
    * Generator for MGF1 as defined in Pkcs 1v2
    */
    public class Mgf1BytesGenerator : IDerivationFunction
    {
        private IDigest digest;
        private byte[]  seed;
        private int     hLen;

        /**
        * @param digest the digest to be used as the source of Generated bytes
        */
        public Mgf1BytesGenerator(
            IDigest  digest)
        {
            this.digest = digest;
            this.hLen = digest.GetDigestSize();
        }

        public void Init(
            IDerivationParameters    parameters)
        {
            if (!(typeof(MgfParameters).IsInstanceOfType(parameters)))
            {
                throw new ArgumentException("MGF parameters required for MGF1Generator");
            }

            MgfParameters   p = (MgfParameters)parameters;

            seed = p.GetSeed();
        }

        /**
        * return the underlying digest.
        */
        public IDigest Digest
        {
            get
            {
                return digest;
            }
        }

        /**
        * int to octet string.
        */
        private void ItoOSP(
            int     i,
            byte[]  sp)
        {
            sp[0] = (byte)((uint) i >> 24);
            sp[1] = (byte)((uint) i >> 16);
            sp[2] = (byte)((uint) i >> 8);
            sp[3] = (byte)((uint) i >> 0);
        }

        /**
        * fill len bytes of the output buffer with bytes Generated from
        * the derivation function.
        *
        * @throws DataLengthException if the out buffer is too small.
        */
        public int GenerateBytes(
            byte[]  output,
            int     outOff,
            int     length)
        {
			if ((output.Length - length) < outOff)
			{
				throw new DataLengthException("output buffer too small");
			}

			byte[]  hashBuf = new byte[hLen];
            byte[]  C = new byte[4];
            int     counter = 0;

            digest.Reset();

			if (length > hLen)
			{
				do
				{
					ItoOSP(counter, C);

					digest.BlockUpdate(seed, 0, seed.Length);
					digest.BlockUpdate(C, 0, C.Length);
					digest.DoFinal(hashBuf, 0);

					Array.Copy(hashBuf, 0, output, outOff + counter * hLen, hLen);
				}
				while (++counter < (length / hLen));
			}

            if ((counter * hLen) < length)
            {
                ItoOSP(counter, C);

                digest.BlockUpdate(seed, 0, seed.Length);
                digest.BlockUpdate(C, 0, C.Length);
                digest.DoFinal(hashBuf, 0);

                Array.Copy(hashBuf, 0, output, outOff + counter * hLen, length - (counter * hLen));
            }

            return length;
        }
    }

}
